Installation

Greeter

You will also need to install a greeter (a user interface for LightDM). The reference greeter is lightdm-gtk-greeter, which is provided by lightdm-gtk3-greeter. KDE users can install lightdm-kde-greeter, a greeter based on Qt.

LightDM can be configured by directly modifying its configuration script or by using the lightdm-set-defaults applications
that can be found in /usr/lib/lightdm/lightdm/. To see some of the options available, execute:

$ man lightdm-set-defaults

There are, however, a lot more variables to modify in the configuration file than by using the lightdm-set-defaults application.

Changing Background Images/Colors

Users wishing to have a flat color (no image) may simply set the background variable to a hex color.

Example:

background=#000000

If you want to use an image instead, see below.

GTK+ Greeter

Users wishing to customize the wallpaper on the greeter screen need to edit /etc/lightdm/lightdm-gtk-greeter.conf defining the background variable.

Note: It is recommended to place the PNG or JPG file in /usr/share/pixmaps since the LightDM user needs read access to the wallpaper file.

KDE Greeter

Go to System Settings > Login Screen (LightDM) and change the background image for your theme.

Changing your avatar

The .face way

Users wishing to customize their image on the greeter screen need to place an image called .face or .face.icon in their home directory. Make sure it can be read by LightDM.

The AccountsService way

The .face way is known to cause issues, fortunately LightDM is able to automatically use AccountsService if it is installed. AccountsService files need to be set up as follows:

A user file named after your user in /var/lib/AccountsService/users/johndoe containing:

[User]
Icon=/var/lib/AccountsService/icons/johndoe

A 96x96 PNG icon file in /var/lib/AccountsService/icons/johndoe

Note: As at June 2013, the PNG icon file does not get picked up and a workaround is to put the file in /usr/share/icons/hicolor/64x64/devices directory and call it from your /var/lib/AccountsService/users/johndoe user file. This directory CAN be read by lightdm and the profile avatar will be rendered correctly.
Also, If using AccountsService, it is not necessary to enable the accounts-daemon.service as it's called automatically with the above configuration.

Sources of Arch-centric 64x64 Icons

The archlinux-artwork package from the official repositories contains some nice examples that install to /usr/share/archlinux/icons and that can be copied to /usr/share/icons/hicolor/64x64/devices as follows:

LightDM goes through PAM even when autologin is enabled. You must be part of the autologin group to be able to login without entering your password:

# groupadd autologin
# gpasswd -a USERNAME autologin

Note: GNOME users, and by extension any gnome-keyring user will have to set up a blank password to their keyring for it to be unlocked automatically.

Hiding system and services users

To prevent system users from showing-up in the login, install the optional dependency accountsservice, or add the user names to /etc/lightdm/users.conf under hidden-users. The first option has the advantage of not needing to updated the list when more users are added or removed.

Troubleshooting

If you encounter consistent screen flashing and ultimately no lightdm on boot, ensure that you have defined the greeter correctly in lightdm's config file. And if you have correctly defined the GTK greeter, make sure the xsessions-directory (default: /usr/share/xsessions) exists and contains at least one .desktop file.

Power menu (restart, poweroff etc.) not available

If you have installed lightdm before lightdm-1:1.6.0-6, you might have been struck by this bug: FS#36613, to fix it run: